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Unformatted text preview: Lecture 5: Kinetic Theory of Gases Equation of State Lets begin by reviewing some of the variables we can use to describe an object, or a system of objects: temperature volume mass pressure All such variables are called state variables i.e., each one tells us something about the state of the system There is another set of variables that describe the flow of energy into or out of the system weve discussed one such transfer variable , heat, in the previous lectures Ideal Gases For a gas, there is no intrinsic volume the gas fills whatever container its placed into An ideal gas is one for which the molecules dont influence each other much e.g., a noble gas at low pressure We can find rules that relate the quantity of gas (in terms of its mass m ) and its pressure, volume and temperature Actually, its often more convenient to express the quantity of gas in moles , defined as: Turns out there are 6.022 x 10 23 molecules in a mole (Avagadros number) n = Molar mass (atomic weight expressed in grams) Equation of State for an Ideal Gas For any gas that is near ideal the following equation of state holds: R is a number that is constant, no matter what type of gas is used the value of this universal gas constant is 8.314 J/mol K We can also write the equation of state in terms of the number of molecules rather than the number of moles: k B is Boltzmanns constant (1.38 x 10-23 J/K) Cross check: PV = PV = Ideal Gas Law R = 8.314 1 6.02 10 23 = 1.38 10-23 = Kinetic Theory of Gases Weve already given the equation of state for an ideal gas:...
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